A repeater using two Integra-TR modems: covering a radio dead zone
The 150-174 MHz VHF channel has one thing that solves everything: radio visibility. A hill, a forest strip, or a valley bend between the facility and the collection point, and the canal is dead. The classic Integra-TR response is a repeater, assembled from two of the same modems: a standard circuit provided by CalAmp DataRadio.
Back-to-back scheme
The two modems connect via the RS-232 port: the first receives the air and transmits data to the second, the second transmits them further to the air. The transparent asynchronous mode of Integra-TR means that the top-level protocol (Modbus, DNP3 and other industrial stacks) passes repeater unchanged - the pollster does not notice the intermediate link.
Receiving and transmitting frequencies on the repeater are spread out so that the transmitter does not clog its own receiver: the sensitivity of 0.35 μV (12 dB SINAD) and the selectivity of 75 dB in the 25 kHz grid give a margin, but duplex decoupling of antennas on the mast is still mandatory - vertical separation or polarization spacing.
What to count before installation
Strip and speed. Each relay takes airtime twice: received - transmitted. At a speed of 19200 bits / s in a grid of 25 kHz and the transmitter attack time of less than 7 ms this is not critical for telemetry, but the number of objects per repeater should be included in the general calculation of the channel - see technical guide “Consultation of objects by radio channel”.
Power supply. Repeater stands tall, often without a network. The modem takes 10–16 V DC: 2600 mA in transmission, 125 mA in reception, less than 20 mA (Rev3) in savings. In an autonomous facility, the budget is counted from the work cycle - a full-time 50% at 5 W (maximum 30 with continuous transmission). Sleep/Suspend modes with less than 100 ms output without data loss allow repeater to be extinguished between polling sessions.
Climate. The operating range from -30 °C to +60 °C closes most of the sites of Russia and Kazakhstan without heating the cabinet; installation - on the DIN-rail inside the sealed glass.
When a repeater is justified
The rule is simple: if bypassing an obstacle with a cellular connection or cable is more expensive than one mast with two modems, a repeater is put. Comparison with a cellular channel on money and availability - in the technical guide "Radiomodem or cellular". Topology of the entire network on 150-174 MHz is analyzed by the article "My own network on Integra-TR".
Both modems for this link are from the warehouse: Integra-TR 242-4018-630 cardThe current availability, condition and conditions of the guarantee are confirmed in the quotation. It is not a public offer.
Frequently asked questions
Why is a repeater made from two modems, rather than a factory?
Integra-TR normally works in such a pair: two modems are connected by RS-232, the first receives ether, the second transmits further. This is a documented CalAmp DataRadio circuit - without a special relay chassis.
Will the SCADA protocol go through repeater without reconfiguring?
Yeah. The modem is transparent asynchronous: Modbus, DNP3 and other industrial protocols are unchanged, the pollster does not see an intermediate link.
Is there enough power supply from the solar panel?
It is calculated from the working cycle: 2600 mA in transmission at 13.3 V, 125 mA in reception, less than 20 mA (Rev3) in savings. Staff cycle 50% at 5 W; Sleep/Suspend modems quench the modem between sessions with output less than 100 ms.
What is the range of the repeater link?
The repeater does not add power – it carries the point of view. The range of each shoulder is considered separately along the highway; in total, the system closes the route where there is no line of sight at all.
